The invention relates to a method of providing an ignitable fuel/air mixture in the cylinders of an internal combustion engine with direct fuel injection, wherein the fuel is injected into the engine combustion chambers by way of an injector including an injection nozzle normally closed by a valve member seated on a valve seat of the injector.
DE OS 43 24 642 A1 discloses an internal combustion engine with direct fuel injection which includes in each cylinder a combustion chamber limited by a piston. A fuel injector is disposed centrally in the top of the combustion chamber to inject fuel into the combustion chamber in a spray beam forming in the combustion chamber an ignitable fuel/air mixture. The electrodes of a spark plug project into a fuel spray beam in the vicinity of the nozzle opening of the injector such that, during low load operation of the internal combustion engine where the engine is operated under stratified charge conditions, the combustion is maintained stable by igniting a fuel-rich mixture in the vicinity of the electrodes of the spark plug. The fuel-rich mixture is provided by injection of the fuel during a later phase of the compression stroke of the piston. The internal combustion engine includes an electronic control unit, which controls the amount of fuel injected by the injector and also the injection timing and the ignition timing for optimal engine operation. The ignition characteristics can be influenced by way of predetermined factors such as injection pressure, shape, and size of the injection nozzle opening, shape of the combustion chamber, compression ratio and so on.
These possible variations of the injection parameters however are, under many operating conditions, not sufficient to insure the optimization of the internal mixture formation with respect to low fuel consumption and low noxious emissions particularly during stratified charge engine operation which occurs over a wide range of the engine performance graph.
It is therefore the object of the present invention to provide a method of generating an ignitable fuel/air mixture in internal combustion engines with direct fuel injection, wherein the internal mixture formation can be optimized under all engine operating conditions and, particularly during stratified charge engine operation.